This invention relates to a composition consisting essentially of a melt-spinnable polymer component and minor amounts of an emulsion polytetrafluoroethylene (E-PTFE) micropowder having a melting point sufficiently far above the processing temperature of the polymer component for the micropowder not to melt during the processing of the polymer component, to the use of such a composition for producing textile fiber material and to the thusly obtained textile fiber material such as filaments, fibers, yarns or fabrics.
Low molecular weight polytetrafluoroethylene (PTFE) having a molecular weight in the range from 104 to 106 g/mol is known as PTFE micropowders or otherwise waxes. In contrast to high molecular weight PTFE having a molecular weight of up to 108 g/mol, such micropowders have virtually no mechanical strength and can therefore not be used as a material of construction in industry. But they are widely used as additives for improving the friction and the nonstick effect, for example in lubricants or in nonstick polishes, where good demolding properties are required. Micropowders are also used in printing inks, chiefly in high gloss printing. As well as enhanced gloss, this provides smoother surfaces and better glide properties for the printed paper (S.V. Gangal, Encyclopedia of Polymer Science and Engineering, Vol. 16, Tetrafluoroethylene Polymers, pages 597 to 598, John Wiley and Sons, 1989).
In these applications, the particle morphology plays a significant role. It is created by the specific production process. Suitable micropowders can also be produced by xcex3-ray or electron beam degradation of high molecular weight E-PTFE. Thermal degradation alters the particle morphology, so that such products are unsuitable for the use according to the invention.
The degraded products are ground to particles 3 to 15 xcexcm in size. The micropowders thus prepared are also known as degradation micropowders. Their preparation is described for example in U.S. Pat. No. 3,766,031, U.S. Pat. No. 3,838,030, U.S. Pat. No. 4,029,870, U.S. Pat. No. 4,036,718 and U.S. Pat. No. 4,052,278.
So-called polymerization micropowders are prepared by free-radical polymerization in aqueous emulsion. An emulsion polymerization is a process in which the monomer (or the monomers)xe2x80x94here tetrafluoroethylene (and optionally small fractions of modifying comonomer)xe2x80x94is reacted at relatively high concentrations of fluorinated emulsifiers such as perfluorooctane acid salts with slow stirring to form a colloidal dispersion. The resulting dispersion having a particle size of about 50 to 400 nm, preferably 100 to 300 nm, in diameter, the so-called primary particle, is coagulated and agglomerated to form a secondary particle 2 to 15 xcexcm in diameter.
Polymerization micropowders are more or less easily disintegratable, which is very advantageous for some applications.
The preparation of such micropowders is described for example in U.S. Pat. No. 2,694,701, U.S. Pat. No. 2,700,661, U.S. Pat. No. 3,067,262, U.S. Pat. No. 3,102,862, U.S. Pat. No. 3,103,490, U.S. Pat. No. 3,105,824 and U.S. Pat. No. 3,956,000.
E-PTFE micropowders are highly crystalline, have a melting point of about 300 to 335xc2x0 C. and a viscosity at 372xc2x0 C. in the range from 101 to 106 Pas, preferably 102 to 105 Pas.
It has now been found that minor amounts, preferably 0.1 to 10% by weight, especially 0.2 to 5% by weight, in particular 0.5 to 3% by weight, of the micropowders substantially improve the production and properties of fibers and filaments. The invention therefore provides appropriate preparations and further concerns preparations in the form of concentrates (xe2x80x9cmasterbatchesxe2x80x9d) which include 10 to 30% by weight, preferably 15 to 25% by weight, of PTFE. These concentrates are diluted with the corresponding spin-processable polymer to the use concentration prior to melt spinning. More particularly and surprisingly, the flex abrasion resistance of the fibers is substantially increased and thereby the further processing into textile structures such as yarns and fabrics improved. The thus finished textiles also exhibit better soil repellence. The addition of micropowders also lowers the apparent viscosity of the melt to be spun, permitting a higher throughput and gentler spinning. These advantages are observed in particular in the spinning of polypropylene.
Useful fiber-forming polymer components include all polymers which are customarily processed in a thermoplastic melt-spinning process, for example polyolefins, polyesters or polyamides, and it is known that the melt may include additives such as color pigments, stabilizers or lubricants.
The processing temperature of spinning or fiber production has to be substantially below the melting point of the micropowder added, i.e. the micropowder should not melt even partially in the course of melt spinning. This is simple to judge from the DSC diagram of the micropowder.
As microscopic examinations of fibers produced according to the invention by addition of micropowders show, the micropowder is surprisingly located virtually exclusively on the surface of the fiber, explaining the beneficial effect of the micropowder with regard to spinning and with regard to the further processing properties. In the course of fiber extrusion, the secondary particle is substantially comminuted and forced to the surface of the fiber.
The micropowder added should not significantly fibrillate during spinning, i.e. the particles must not undergo streamlining. This inhibits or suppresses the transport to the fiber surface. Micropowder particle fibrillation can be suppressed by lowering the molecular weight to below 8xc2x7105 g/mol, which corresponds to a melt viscosity of 105 Pas. Micropowders having this molecular weight are therefore preferred.
The micropowder added should also contain as little as possible of auxiliary chemicals and chemically aggressive end groups from the production process. At the processing temperature these components can degrade the polymer component, for example in the case of polyesters, or chemically alter the usually necessary additives such as stabilizers, dyes or lubricants. PTFE micropowders should in particular be free of carboxyl fluoride COF groups, as generated in the course of radiation degradation in particular. Such products are therefore advantageously aftertreated in known manner. In the case of polymerization micropowders, treatment with ammonia is an advantageous way of generating neutral carboxylamide CONH2 end groups (EP-A-0 780 403).
The PTFE micropowder is essentially a tetrafluoroethylene homopolymer which may also be slightly modified with other comonomers. Useful comonomers include all olefins capable of copolymerizing with tetrafluoroethylene, for example hexafluoropropylene, perfluorooxyalkyl vinyl ethers having alkyl radicals of 1 to 4 carbon atoms, vinylidene fluoride, ethylene or propylene. This xe2x80x9cmodificationxe2x80x9d can also be effected by means of vinyl esters and acrylic monomers. The degree of modification should not exceed 0.3 mol %, preferably 0.1 mol %, in order that the chemical character and the physical properties of the PTFE micropowder may be substantially retained and the polymer may not be formable from the melt. The modified micropowder, like the unmodified micropowder, should be chemically inert and at most interact minimally with the components of the spinning melt.